Process and device for the manufacture of mouldings

ABSTRACT

In a process for the manufacture of mouldings, especially optical lenses, specifically contact lenses (CL), a starting material that is crosslinkable by the impingement of suitable energy is introduced into a mould (1) having a cavity (15), which mould is at least partially permeable to the energy concerned. The starting material is introduced into the cavity in a still at least partially uncrosslinked state, the mould cavity determining the shape of the moulding (CL) to be produced. By means of impingement of the energy concerned, the starting material is crosslinked to an extent sufficient for it to be possible for the moulding (CL) to be released from the mould. The filling of the mould cavity is carried out in the starting material that is still at least partially in the uncrosslinked state.

This is a continuation of application Ser. No. 08/278,477 filed on Jul.20, 1994, now abandoned.

Foreign priority is claimed under 35 USC 119 to Swiss Patent ApplicationNo. 2299/93-3, filed on Jul. 29, 1993; and Swiss Patent Application No.2350/93-0, filed on Aug. 6, 1993.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process for the manufacture of mouldings,especially optical lenses and specifically contact lenses, in accordancewith the preamble of the respective independent patent claim. Theinvention furthermore relates to mouldings, especially optical lensesand specifically contact lenses, manufactured in accordance with thatprocess or by means of that device.

2. Related Art

Contact lenses that are to be manufactured economically in large numbersare preferably produced by so-called mould processes and specifically bythe full-mould process. In those processes, the lenses are manufacturedin their final form usually between two mould halves (moulds), so thatneither subsequent machining of the surfaces of the lenses nor machiningof the rim is necessary. Mould processes are known, for example, fromWO-A-87/04390 and from EP-A-0 367 513.

In those known mould processes, the geometry of the contact lens that isto be produced is determined by the mould cavity. The rim of the contactlens is also formed by the mould, which usually consists of two mouldhalves. The geometry of the rim is determined by the contour of the twomould halves in the region in which they are in contact with oneanother.

In order to produce a contact lens, first of all a determined amount ofa flowable starting material is introduced into the female mould half.The mould is then closed by applying the male mould half. Normally, thestarting material is supplied in slight excess, so that the excessamount is forced into an overflow chamber externally adjacent to themould cavity when the mould is closed. The subsequent polymerisation orcrosslinking of the starting material is effected by irradiation with UVlight or by thermal action or by another, non-thermal, method, duringthe course of which both the starting material in the mould cavity andthe excess material in the overflow chamber are fully cured. The fullcure of the excess material may be delayed slightly, since it mayinitially be inhibited by atmospheric oxygen. In order to achievefault-free separation of the contact lens from the excess material, theexcess material must be well sealed off or expelled from the zone inwhich the two mould halves are in contact with one another. Only in thatmanner is it possible to obtain fault-free contact lens rims.

The materials currently used for the moulds are preferably plastics,such as, for example, polypropylene. The moulds are produced byinjection moulding and used only once (disposable moulds). The reasonsfor this are, inter alia, that the moulds are in some cases contaminatedby the excess material, are damaged when the contact lens is separated,or are irreversibly deformed in some areas.

In the case of injection-moulded moulds, variations in the dimensionsmust also be expected as a result of variations in the manufacturingprocess (temperatures, pressures, material properties). Shrinkage of themoulds may also occur after injection moulding. The dimensionalvariations in the mould may lead to variations in the parameters of thecontact lens being produced (vertex refractive power, diameter, basecurve, middle thickness etc.), which may have an adverse effect on thequality of the lenses and thus result in a reduced yield. If the sealbetween the mould halves is inadequate, the excess material is notcleanly separated, which results in the formation of so-called flash atthe contact lens rim. Where that is relatively pronounced, such acosmetic fault at the rim of the lens may also cause irritation to thewearer, and such lenses therefore have to be identified by inspectionand removed.

Particularly in view of the quality requirements of the contact lensrim, the moulds are also used only once, because it is not possible torule out absolutely a certain deformation of the moulds in the region inwhich they are in contact with one another.

A further mould process for the manufacture of, inter alia, contactlenses is described in U.S. Pat. No. 4,113,224. That process uses amould in which the cavity is not completely sealed but is connected by athin annular gap to a reservoir channel (overflow channel) surroundingthe cavity. During the crosslinking process, material can flow back outof the reservoir through the annular gap and into the mould cavity tocompensate for the relatively large shrinkage in volume which occurswith the lens materials customarily used.

The material in the reservoir channel can be prevented from crosslinkingby an inhibiting gas atmosphere or by being shielded from the energyradiation causing the crosslinking. To ensure that material flows backinto the mould cavity, the material located in the mould cavity is, atleast to begin with, subjected to radiation only in a central region,which is smaller than the diameter of the mould cavity, or is exposed toa stronger intensity of radiation in that central region than in theedge region of the mould cavity surrounding that central region. Aftercrosslinking has commenced in the central region and has progressed to acertain degree, however, the material disposed in the edge region andthe adjacent annular gap, and that located in the reservoir channel, isalso exposed to the full radiation and crosslinked. The burrs and flashmentioned further above are inevitably formed, so that the mouldings orcontact lenses manufactured by that known process require subsequentmachining.

A further problem arising during manufacture according to processesdescribed hitherto is that air inclusions may occur when the mould isclosed. Air inclusions in the lenses result, however, in the lensesbeing identified as rejects in the subsequent inspection (qualitycontrol). The mould has hitherto been closed correspondingly slowly, soas to enable the air to escape as fully as possible from the mouldcavity. The comparatively slow closure of the mould, however, takes up arelatively large amount of time.

SUMMARY OF THE INVENTION

The aim of the invention is therefore to provide a process and a deviceof the kind mentioned in which, inter alia, the degree of efficiency ishigh, that is to say the mould can be used efficiently, and in whichexpenditure is comparatively low, but always with the proviso that themoulding (e.g. contact lens) produced is free from air inclusions.

In respect of the process, that aim is achieved by carrying out thefilling of the mould cavity in the starting material that is still atleast partially in the uncrosslinked state. As a result, right from thebeginning, when the mould is being filled, there can be no air in themould, and so air inclusions are completely avoided. The mould canconsequently be closed more quickly, and thus used more efficiently,while at the same time expenditure is comparatively very low.Furthermore, in that manner an exact measurement of the required amountof starting material is provided automatically, since the filling takesplace in the starting material.

In one variant of the process, for the purpose of filling the mouldcavity, the cavity can be connected to a reservoir which surrounds it,in which the starting material is stored and from which the mould cavityis flooded. This is a process variant that is especially uncomplicatedtechnologically.

In a further process variant, the mould is also closed in the startingmaterial so as to exclude the risk of air in any way getting into themould cavity during the closing operation.

In a further variant, a mould is used that comprises a container and amould member displaceable in the manner of a piston in that container.The mould member can be moved away from and towards the container walllying opposite it for the purpose of opening and closing the mould.Starting material is fed in between the container wall and the mouldmember as the mould is opened and conveyed away again as the mould isclosed. As a result of the movement of the displaceable mould memberaway from the opposite-lying container wall the space between thedisplaceable mould member and the container wall is filled with startingmaterial without air being able to penetrate into that space.Subsequently, as a result of the movement of the displaceable mouldmember towards the container wall, the starting material disposedbetween the mould member and the container wall is conveyed away again,the material located in the mould cavity naturally remaining there. Itis also impossible for any air to enter the mould cavity as the mouldmember moves towards the container wall, as a result of which mouldingsthat are free from air inclusions can be produced in a simple andefficient manner.

For example, a mould having two mould halves may be used in which onemould half is provided on the container wall and the other mould half isprovided on the displaceable mould member. In that arrangement a mouldhaving a male mould half and a female mould half may be used, the malemould half being provided on the container wall and the female mouldhalf on the displaceable mould member. Pumps may advantageously be usedto feed in and convey away the starting material. In a furtheradvantageous process variant, the piston may be driven in order to feedin and convey away the starting material.

The crosslinked moulding can be removed from the mould in an especiallysimple manner by flushing out the mould with starting material. This canbe effected, for example, by the moulding being separated from the mouldby the flow of starting material as the mould is opened and beingflushed out of the mould by the flow of starting material as the mouldis closed.

In one variant of the process, in a first cycle the mould is opened andclosed again. Subsequently, at least the crosslinking necessary for itto be possible for the moulding to be released from the mould iseffected by the action of energy. In a second cycle the mould is openedagain, the moulding being separated from the mould. The piston-likemould member is then moved towards the opposite-lying container wallagain and the mould is thus closed again, the crosslinked moulding beingflushed out of the mould. This "two-cycle" variant of the process isdistinguished by the fact that the moulding is produced in the firstcycle and then flushed out of the mould in a second cycle. The mould cansimultaneously be cleaned in the "flushing cycle".

The process variant just described can be carried out either byproviding first a "production cycle" (first cycle) and then a separate"flushing cycle" (second cycle, for example using a flushing liquid), oralternatively the flushing can be arranged to coincide with theproduction cycle of a new moulding, that is to say as new startingmaterial is introduced into the mould cavity the moulding produced inthe preceding cycle is flushed out of the mould. The "two-cycle" variantof the process then becomes a "single-cycle" variant.

The crosslinked moulding can, however, also be removed from the mould bymeans of a gripping device. This can be effected by depositing themoulding removed from the mould by the gripping device on thedisplaceable mould member outside the space between the displaceablemould member and the opposite-lying container wall. The mouldingdeposited on the displaceable mould member can be held fast thereto bynegative pressure and then released from it again by positive pressure.

In a further process variant, the mould is not completely closed afterthe starting material has been introduced into the mould cavity, so thatan annular gap containing uncrosslinked starting material, which gapsurrounds the mould cavity and is in communication with that mouldcavity, remains open. By this means on the one hand a shrinkage involume occurring during crosslinking can be compensated by startingmaterial flowing back through the annular gap into the mould cavity, andon the other hand the mould halves are prevented from being pressed hardagainst one another during manufacture of the moulding. Especially inview of the risk of the mould halves being irreversibly deformed bymechanical stress, mould halves have hitherto been used only once, asexplained in the introduction. In accordance with this process variant,the mould halves can be used repeatedly.

It is also conceivable for the mould to be closed further followingcrosslinking shrinkage as crosslinking of the material progresses.

It is, however, in any event important to use a starting material thatis of at least viscous flowability prior to the crosslinking, so thatstarting material can flow back through the annular gap into the mouldcavity to compensate for shrinkage.

According to a further process variant, the impingement upon thematerial of the energy causing crosslinking is restricted spatially tothe region of the mould cavity, so that substantially only the startingmaterial located in the mould cavity, that is to say the region of themoulding, specifically of the contact lens, is crosslinked. Any excessstarting material present is not polymerised or crosslinked. In thatarrangement, partial areas of the moulding rim are formed not by amechanical limitation of the material by mould walls but by a spatialrestriction of the impinging energy (usually UV or some other radiation)that triggers the polymerisation or crosslinking. As a result of thosetwo measures, contact between the two mould halves can in a preferredarrangement be avoided, so that they are not deformed and canaccordingly be used again. In addition, the known problem of volumeshrinkage which occurs during crosslinking can also be dealt with verysimply thereby without it being necessary, as in the case, for example,of U.S. Pat No. 4,113,224, for the moulding to be mechanically processedsubsequently.

In one process variant, the spatial restriction of the energyimpingement is effected by masking for the mould that is at leastpartially impermeable to the particular form of energy used. The energyused for the crosslinking is radiation energy, especially UV radiation,gamma radiation, electron radiation or thermal radiation, the radiationenergy preferably being in the form of a substantially parallel beam inorder on the one hand to achieve good restriction and on the other handefficient use of the energy.

In a further variant, the mould used is one that is highly permeable, atleast at one side, to the energy form causing the crosslinking. Thespatial restriction of the energy impingement is effected by parts ofthe mould that are impermeable or of poor permeability to the energyform.

In a further variant of the process the mould used is one that is highlypermeable, at least from one direction, to the energy form causing thecrosslinking. The spatial restriction of the energy impingement iseffected by a mask that is impermeable or of poor permeability to theenergy and that is provided outside the mould cavity on or in the mould.

In that arrangement the mask is preferably arranged in the region of theseparating planes or separating faces of different parts of the mould,especially in regions of those parts that are in contact with thecrosslinkable starting material.

In a further process variant, the energy causing the crosslinking iskept away from the starting material disposed in the annular gap, sothat the crosslinking can occur in the mould cavity only and so that itis possible especially for starting material to flow back in order tocompensate for the volume shrinkage. The mould can also be closedfurther following crosslinking shrinkage as crosslinking of the materialprogresses.

In that arrangement a material that is of at least viscous flowabilityprior to crosslinking is used, so that starting material can flow backthrough the annular gap into the mould cavity to compensate forshrinkage. If, after the moulding has been released from the mould,there is any uncrosslinked material still adhering to it, that materialcan be removed by washing with a suitable solvent. In any event,however, subsequent mechanical processing of the moulding is dispensedwith.

In respect of the device, the aim of the invention is achieved byarranging the mould cavity, during filling, in starting material that isstill at least partially in the uncrosslinked state. As a result, rightfrom the beginning, when the mould is being filled, there can be no airin the mould, and so air inclusions are completely avoided. The mouldcan consequently be closed more quickly and thus used more efficiently,while at the same time expenditure is comparatively very low.

In one example embodiment the device comprises a reservoir for supplyingthe starting material that surrounds the mould cavity. The reservoir canbe connected to the mould cavity. When the mould cavity is being filled,the reservoir is connected to the mould cavity and floods that cavity.This allows several structurally especially simple further developments,which will be explained in more precise detail.

In a further example embodiment, the device comprises means for closingthe mould which is arranged in the starting material, the mould, in thiscase too, always being closed in the starting material so that no aircan enter the mould cavity.

In an advantageous example embodiment, the mould comprises a containerand a mould member displaceable in the manner of a piston in thatcontainer, which mould member can be moved away from and towards thecontainer wall lying opposite it for the purpose of opening and closingthe mould. Provided in the container is an inlet through which startingmaterial flows in between the container wall and the mould member as themould is opened. Also provided in the container is an outlet throughwhich starting material flows out again as the mould is closed. Thisexample embodiment is structurally comparatively simple, that is to saynot very complicated, and is therefore well suited to practical use.

The mould in that arrangement preferably has two mould halves, one mouldhalf being provided on the container wall and the other on thedisplaceable mould member. The mould has (especially in the manufactureof contact lenses) a male mould half and a female mould half.Preferably, the male mould half is provided on the container wall andthe female mould half on the displaceable mould member. In thatarrangement the moulding (contact lens) can later be released from themould especially simply.

Pumps are preferably provided for feeding in and/or conveying awaystarting material which, as the mould is opened, feed in startingmaterial through the inlet and between the container wall and the mouldmember and, as the mould is closed, convey it back through the outlet.Such pumps operate reliably and therefore do not represent any specialexpenditure.

In a further example embodiment, means are provided for driving themould member that is displaceable in the manner of a piston. Those meansmay be provided, both in a device that works without and in a devicethat works with pumps, for the purpose of moving the mould memberdisplaceable in the manner of a piston in the direction towards theopposite-lying container wall and thus forcing starting materialdisposed between the mould halves out again.

In a further example embodiment of the device, means are provided forproducing a flow. That flow separates the moulding from the mould whenthe mould is opened and flushes the moulding out of the mould when themould is closed. Those means may be in the form of jets or similarlyacting means. It is important that they produce a flow or a turbulencein the starting material disposed between the mould halves so that themoulding (contact lens) is lifted off the mould half by means of theflow or turbulence.

In a further example embodiment of the device, in a first cycle("production cycle") starting material first of all flows in through theinlet and between the container wall and the displaceable mould memberand then flows back out through the outlet. The energy source then actsupon the mould with an amount of energy necessary for it to be possiblefor the moulding to be released from the mould, so that crosslinkingoccurs. Then, in a second cycle, for example starting material againflows in through the inlet and between the container wall and thedisplaceable mould member, separates the moulding from the mould andflushes it out through the outlet.

That "two-cycle" device is distinguished by the fact that in the firstcycle the moulding is produced, and then in the second cycle (flushingcycle, cleaning cycle) the moulding is flushed out of the mould and themould is also simultaneously cleaned.

That device may either be so constructed that, as described, there isfirst of all a "production cycle" (first cycle) and then a separate"flushing cycle" (second cycle), or alternatively it may be soconstructed that the flushing out coincides with the production cycle ofa new moulding, that is to say, as new starting material is introducedinto the mould cavity, the moulding produced in the preceding cycle isflushed out of the mould. The "two-cycle" device then becomes a"single-cycle" device. In the "single-cycle" device, however, startingmaterial must be used for flushing, whereas in the "two-cycle" devicethe use of a special cleaning liquid in the flushing cycle is alsopossible.

To remove the moulding, a gripping device may be provided that removesthe crosslinked moulding from the mould. For that purpose the containerpreferably has on a container wall other than the shape-giving face ahollow or recess that extends substantially in the direction of movementof the displaceable mould member. The gripping device is arranged inthat hollow or recess. The displaceable mould member comprises, on anouter wall that does not lie opposite the shape-giving container wall,an indentation in which the gripping device deposits the removedmoulding. This is a structurally especially advantageous and simplearrangement of the device.

In a possible further development of that device the displaceable mouldmember comprises a channel that leads to the indentation and can beconnected to a negative pressure or positive pressure source. Thechannel is connected to the negative pressure source when the grippingdevice deposits the removed moulding in the indentation of the mouldmember. In order to release the lens it is then connected to thepositive pressure source. By this means the lens can be produced duringone cycle and removed, deposited on the mould member and then taken offthe mould member during the next cycle. This is possible both in adevice constructed as a "two-cycle" device and in a device constructedas a "single-cycle" device.

In a further example embodiment of the device, the mould is providedwith spacers that hold the two mould halves a small distance apart fromone another when the mould is in the closed position, so that an annulargap that surrounds the mould cavity and is in communication therewith isformed.

By that means, on the one hand volume shrinkage occurring duringcrosslinking can be compensated, since starting material can flow backinto the mould cavity through the annular gap. On the other hand thespacers prevent the mould halves from being pressed hard against oneanother during production of the moulding. Particularly in view of therisk of the mould halves being irreversibly deformed as a result ofmechanical stress, mould halves have hitherto been used only once, asexplained in the introduction. Using this example embodiment of thedevice it is possible for the mould halves to be used repeatedly. It isfurthermore possible in a further development of the device for themould to be provided with resilient means or displacement means thatallow the two mould halves to move closer together followingcrosslinking shrinkage.

In a further example embodiment, means are provided that restrict theimpingement of energy upon the mould to the region of the mould cavity,so that substantially only the starting material located in the mouldcavity, that is to say the region of the moulding, specifically of thecontact lens, is crosslinked. Any excess starting material present isnot polymerised or crosslinked. In that arrangement, partial areas ofthe moulding rim are formed not by a mechanical limitation of thematerial by mould walls but by a spatial restriction of the impingingenergy (usually UV radiation or another form of radiation) that triggersthe polymerisation or crosslinking. As a result of those two measures,in a preferred arrangement contact between the two mould halves can beavoided, so that they are not deformed and can accordingly be usedagain. In addition, the known problem of volume shrinkage which occursduring crosslinking can be dealt with very simply thereby without itbeing necessary, as in the case, for example, of U.S. Pat. No.4,113,224, for the moulding to be mechanically processed subsequently.

In a further development of the example embodiment just mentioned, themould is provided with a mask that is impermeable or of poorpermeability to the energy, which mask screens from the energy allcavities, with the exception of the mould cavity, that may containuncrosslinked material and all mould faces that may come into contactwith the material. In that arrangement the mould may comprise two mouldhalves that are separated along a separating face, and the mask isarranged outside the mould cavity on one of the two mould halves and/oron both mould halves in the region of the separating face.

In a further example embodiment of the device, the energy sourceproduces UV-radiation, and at least one of the halves of the mouldconsists of UV-permeable material, especially quartz. The mask in thatarrangement may consist of a layer of material that is impermeable to UVradiation, especially a chrome layer. In the example embodiment of thedevice having an annular gap, the mask may be arranged in the region ofthe annular gap.

In the example embodiments of the device in which the crosslinking isrestricted spatially to the region of the mould cavity, the mould maynaturally also be provided with resilient means or displacement meansthat allow the two mould halves to move closer together followingcrosslinking shrinkage.

In particular, mouldings, especially optical lenses and specificallycontact lenses, can be manufactured in accordance with the process andusing the device described.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail in the following with reference tothe drawings, which are at least partly in diagrammatic form or insection.

FIGS. 1A-1C show an example embodiment of the device according to theinvention,

FIGS. 2A-2C show a further example embodiment of the device according tothe invention,

FIGS. 3A-3C show a variant of the example embodiment of FIG. 2,

FIGS. 4A-4C show a further example embodiment of the device according tothe invention, and

FIG. 5 is an enlarged illustration of the rim area of an exampleembodiment of a mould in the closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The example embodiment of the device according to the invention shown inFIGS. 1A-C is designed for the manufacture of contact lenses from aliquid starting material that can be polymerised or crosslinked, forexample, by UV radiation. FIG. 1A shows the mould 1 in the closedposition. The mould 1 is arranged in a container 10 that is full ofuncrosslinked liquid starting material M. The device furthermorecomprises an energy source in the form of a UV light source 2a, and alsomeans 2b that direct the energy supplied by the UV light source 2a ontothe mould 1 in the form of a parallel beam 3. Those means 2b mayespecially also comprise a shutter that is arranged between the UV lightsource 2a and the container 10. The UV light source 2a and the means 2bcan obviously also be combined into a single unit.

Details on the general construction and on questions concerningdimensions, material and stability etc., as well as, for example, onsuitable materials for the mouldings and on aspects concerningprocessing technology, are dealt with very comprehensively in EP-A-O367513 and especially in U.S. Pat. No. 4,113,224, and those documents aretherefore expressly declared to be an integral part of the presentdescription (incorporation by reference).

The mould 1 comprises two mould halves 11 and 12, each of which has acurved mould face 13 and 14, respectively, which together define a mouldcavity 15 which in turn determines the shape of the contact lens CL tobe produced. The face 13 of the upper mould half 11 is concave anddetermines the front face with the rim area adjacent thereto. That mouldhalf 11 is usually referred to as the female mould half. The face 14 ofthe lower mould half 12 is convex and determines the rear or base faceof the contact lens, and the rim area thereof adjacent thereto. Thatmould half 12 is usually referred to as the male mould half.

Unlike the moulds known, for example, from the documents WO-A-87/04390or EP-A-0 367 513 mentioned in the introduction, the mould cavity is notcompletely and tightly sealed but, in the example embodiment shown, isopen all the way round in the region of its circumferential rim, whichdefines the rim of the contact lens CL to be produced. The mould cavity15 is also in communication there with a relatively narrow annular gap16, as is also the case in the moulds shown in U.S. Pat. No. 4,113,224.The annular gap 16 is limited by a flat mould wall 17 on the femalemould half 1 and a flat mould wall 18 on the male mould half 12. Toprevent complete closure of the mould, spacers in the form of spacerbolts 19 are provided on the male mould half 12 which keep the femalemould half 11 at a distance, that is to say prevent complete closure ofthe mould and thus define the annular gap 16. The spacer bolts may beadjustable (for example by means of a thread not shown, provided in themale mould half) or may alternatively be of resilient construction. Inthat manner the two mould halves 11 and 12 can be moved towards oneanother during the crosslinking operation by adjusting the spacers oragainst a resilient force in order to compensate for shrinkage. Themould can obviously be opened and closed in the usual manner, forexample by means of a closing unit indicated here by the arrow 1a only.Adjustment of the distance between the two mould halves to compensatefor shrinkage can also be carried out, for example, by means of thatexternal closing unit.

In another arrangement, not shown here, a number of segment-shaped gapsmay be provided instead of the continuous annular gap 16 and the spacers19, the intermediate spaces between the individual segment gaps takingover the function of the spacers. Obviously, other configurations arealso possible.

The two mould halves 11 and 12 consist of a material that is aspermeable as possible to the selected energy, which in this case, asalready mentioned, is, for example, UV light, for example they consistof polypropylene usually used for such purposes or of anotherpolyolefin. Since the irradiation with UV light is in this case from oneside only, that is from above, it is actually necessary only for theupper, that is to say in this case the female, mould half 11 to beUV-permeable. Obviously, the same applies also for irradiation frombelow through the male mould half 12. According to an especiallyexpedient and advantageous arrangement of the invention, at least themould half that is irradiated with UV light consists of quartz. Not onlydoes that material have especially good UV permeability but it is alsovery hard and resistant, so that moulds made from it can very readily bereused. A prerequisite for that, however, which is disclosed in furtherdetail in the following, is that the mould is closed either withoutforce or not fully, so that the mould halves are not damaged by contact.UV-permeable special glasses or sapphire are possible alternatives toquartz. On account of the fact that the mould or mould halves can bere-used, expenditure on their manufacture may be relatively high inorder to obtain moulds of extremely high precision and reproducibility.Since the mould halves do not touch in the region of the lens beingproduced, that is to say in the region of the mould cavity 15 or of theactual mould faces, damage by contact is excluded. A high degree ofdurability of the moulds is thereby assured. This also has favourableconsequences in general for the reproducibility of the contact lenses ormouldings being produced.

The space between the two mould halves 11 and 12 and thus also the mouldcavity 15 is arranged in the uncrosslinked starting material M for theentire production process. In accordance with the general concept of theinvention, in any event at least the mould cavity is arranged completelyin the starting material in its uncrosslinked state during filling. FIG.1B shows that the upper mould half 11, even in the opened position, isnot completely clear of the starting material M, the space between themould halves 11 and 12 always remaining below the liquid surface of thestarting material M disposed in the container 10. Consequently, thespace between the two mould halves, and especially also the mouldcavity, are always in communication with the starting material Mdisposed in the container 10. As a result air can at no time enter thespace between the two mould halves 11 and 12.

When the mould cavity is full and the mould is closed (FIG. 1A), themould is impinged upon by UV rays 3 and the moulding is thuscrosslinked.

After crosslinking, the mould is opened and the moulding in the form ofthe contact lens CL is released from the mould, that is to say taken offand removed from the mould. There is shown symbolically in FIG. 1C forthat purpose a gripping device 4 which, when the upper mould half hasbeen raised, takes the contact lens CL off the male mould half 12 (FIG.1B) and removes it from the mould (FIG. 1C). The release and removal ofthe contact lens or moulding from the mould may, however, also becarried out by other means, as will be explained by way of the otherexample embodiments. After removal of the contact lens or moulding, themould can be closed again and a new contact lens CL produced.

Since the entire production process according to FIGS. 1A-C takes placebelow the liquid surface of the starting material M in the container 10,no air can enter the space between the two mould halves 11 and 12 or, inparticular, the mould cavity 15. Since the mould is opened and closedbelow the liquid surface, the mould can also be closed comparativelyquickly, which was not possible with the processes and devices accordingto the state of the art. It is thus possible for contact lenses that arefree from any air inclusions to be produced efficiently and with lowexpenditure.

In the example embodiment shown in FIGS. 1A-C, in addition impingementof UV rays upon the mould is restricted to the material in the mouldcavity 15, that is to say only the material disposed in the mould cavity15 is crosslinked. In particular, the starting material in the annulargap 16, which surrounds the mould cavity 15, and the remainder of thestarting material M disposed in the container 10 are not impinged uponby energy and are not crosslinked. "Mould cavity" therefore here denotesthat cavity of the closed mould which is defined by the complete contourof the moulding to be produced, specifically therefore the contact lensCL. The annular gap 16 opening into the mould cavity does not,therefore, form part of the mould cavity 15 here.

For realisation in practice, according to FIGS. 1A-C there is providedon the mould wall 17, in the region of the annular gap 16, a mask 21that is impermeable (or at least of poor permeability compared with thepermeability of the mould) to the energy used, in this case therefore UVlight, which mask extends right up to the mould cavity and, with theexception of the mould cavity, screens from the radiated energy allremaining parts, cavities or surfaces of the mould that are in contactwith or may come into contact with the here liquid uncrosslinked,possibly excess, material. Partial areas of the lens rim are formed notby a limitation of the material by mould walls but by a spatialrestriction of the radiation or other energy triggering polymerisationor crosslinking. The side walls of the upper mould half are alsoprovided with the mask 21 so as to prevent the starting material M thatsurrounds the mould in the container 10 from being crosslinked.

In the case of UV light, the mask may preferably be a thin chrome layer,which can be produced according to processes as known, for example, inphoto and UV lithography. Other metals or metal oxides may also besuitable mask materials. The mask can also be coated with a protectivelayer, for example of silicon dioxide if the material used for the mouldor mould half is quartz. The mask does not necessarily have to be fixedbut could, for example, be constructed or arranged to be removable orexchangeable. It could, in principle, be provided anywhere at or on themould as long as it was able to fulfill the function for which it wasintended, namely the screening of all areas of the mould carryinguncrosslinked material with the exception of the mould cavity.Preferably, the mask is arranged on, or just below, a wall surface thatis in contact with the uncrosslinked starting material, since in thatmanner undesired diffraction and scattering effects can be substantiallyexcluded. That is not, however, absolutely essential. In principle it iseven possible to dispense with a mask or masking in or on the mould ifthe energy impingement can be restricted locally to the mould cavity bysome other means, where necessary taking into consideration the opticaleffect of the mould. In the case of UV radiation this could be achieved,for example, by a spatially restricted light source, a suitable lensarrangement optionally in combination with external masks, screens orthe like and taking into consideration the optical effect of the mould.

A further example embodiment of the device according to the invention isshown in FIGS. 2A-C. In that example embodiment one mould half, in thiscase the male mould half, is formed by one wall of a container 10a, inthis case the container base 100a. The male mould half is thus formeddirectly on the container base 100a. Also provided in the container 10ais a mould member 11a displaceable in the manner of a piston, which canbe moved away from the container wall lying opposite it, in this casethe container base 100a, and back towards the container base, whilemaintaining a seal along the side walls of the container. The mould cantherefore be opened and closed in that manner. The mould member 11a iscorrespondingly formed as the female mould half on its face 17a thatfaces the container base. Container base 100a and mould face 17a definethe mould cavity 15a when the mould is in the closed position (FIG. 2A).Naturally, the mould member does not necessarily have to be constructedin the form of a piston and it would equally be possible for a diaphragmto be provided to which the mould half was attached. Other methods ofaltering the volume are also possible.

Provided in the container 10a, in this case the container base 100a, isan inlet 101a through which starting material can flow into the spacebetween the mould member 11a and the container base 100a. The spacebetween the mould member 11a and the container base 100a is for thatpurpose continuously in communication with a reservoir R. By means ofpumps P1 and P2 at the inlet 101a and outlet 102a respectively, startingmaterial can be conveyed to and from the space between mould member 11aand container base 100a, it being important for the space between mouldmember 11a and container base 100a always to be filled with startingmaterial M so that no air can penetrate into that space. The pumps P1and P2 are represented with an integrated non-return valve, but it isalso possible to use pumps without an integrated non-return valve and toconnect the valve separately between pump and container or, depending onthe type of pump, to dispense with such a non-return valve completely.

When the mould is in the closed position (FIG. 2A), it is impinged uponby energy, in this case again UV radiation 3. In this case, too, theimpingement of energy upon the mould is, for example, from above.Crosslinking is caused thereby. The crosslinked moulding CL is thenlifted from the mould and removed from the mould. For that purpose,first of all liquid starting material M is fed by means of the pump P1through the inlet 101a into the space between the container base 100aand the mould member 11a, and the piston-like mould member 11a is movedupwards (FIG. 2B). The moulding, in this case in the form of the contactlens CL, can then be separated from the mould and removed. That can beeffected, for example, by means of a special gripping device, as alreadydescribed with reference to FIG. 1. The contact lens CL can, however,equally be flushed out of the mould, as will be explained in more detailin the following.

The mould member 11a displaceable in the manner of a piston is thenmoved downwards again and the material disposed between the mould member11a and the container base 100a is conveyed away through the outlet 102a(FIG. 2C). The material can be conveyed away by means of the pump P2provided at the outlet.

It is, in principle, possible here for the mould member 11a displaceablein the manner of a piston to be driven solely by the liquid startingmaterial fed in and conveyed away from between mould member 11a andcontainer base 100a, so that the pumps P1 and P2 supply the drivingenergy necessary therefor. It is also possible for there to be no pumpsat all and for the mould member 11a displaceable in the manner of apiston to be driven mechanically, that is to say for starting materialto be sucked in during the upward movement and forced back out againduring the downward movement. Obviously combinations with pumps and amechanical drive are also possible.

A mask 21a is provided on the mould member 11a. In a similar manner tothat described for the upper mould half 11 in FIGS. 1A-C, it extendsover the annular gap 16a up to the mould cavity 15a, and also optionallyalong the side walls of the mould member 11a displaceable in the mannerof a piston. If the mould is then impinged upon by UV radiation 3,crosslinking occurs in the region of the mould cavity 15a only, withconsequent formation of the moulding. The material in the remainingareas, especially in the annular gap 16a, and also other startingmaterial in the container 10a, is not cross-linked. In principle, thesame considerations in respect of the materials and the production andmounting of such masks as those already made in the explanations ofFIGS. 1A-C apply here too.

FIGS. 3A-C show an example embodiment of the device that in principle isvery similar to the example embodiment of FIGS. 2A-C. One difference,however, is that no pump P2 is provided at the outlet 102a in theexample embodiment according to FIGS. 3A-C, but the outlet 102a isconstructed as a deformable flap or plate or as a trap door. In theexplanation of FIGS. 3A-C, especially the release from the mould of themoulding, in this case therefore of the contact lens CL, will bedescribed in detail in the following. The filling of the mould cavity15a is carried out analogously to the example embodiment according toFIGS. 2A-C by means of the pump P1. When the mould is in the closedposition (FIG. 3A), the contact lens CL is produced by crosslinking byimpingement of UV radiation 3 upon the mould.

As the piston-like mould member 11a (FIG. 3B) moves upwards, liquidstarting material flows into the container 10a between the containerbase 100a and the mould member 11a displaceable in the manner of apiston. The inlet 101a may be constructed as a jet or similarly actingflow-producing means. As the liquid starting material is fed through theinlet, the crosslinked contact lens CL is lifted from the mould by theflow produced and, with appropriate arrangement of the jet, is flushedtowards the outlet 102a, which in this case is constructed as adeformable flap or plate. During the downward movement of thepiston-like mould member 11a (FIG. 3C), the flap is deformed downwardsby the pressure generated and opens the outlet 102a, so that the liquidstarting material together with the contact lens CL can be flushed outthrough the outlet 102a. The contact lens can be collected in a sieve Sthat is permeable to the liquid starting material. The starting materialmay, for example, be recycled and reused, where necessary after it hasbeen cleaned. While the contact lens is being flushed out, the mouldcavity 15a is filled with new starting material, so that a new contactlens CL can immediately be crosslinked by the impingement of UVradiation 3.

It has been described above that, for the purpose of lifting off andflushing out, liquid starting material is fed into the container 10a, inthe same cycle the mould cavity 15a is filled again and, with the mouldin the closed position, the mould is again impinged upon by UV radiation3 for the purpose of crosslinking and producing the next contact lensCL. The device thus operates, as it were, as a "single-cycle" device,since in each cycle (upward and downward movement of the piston-likemould member 11a) a contact lens is produced and flushed out of themould.

It is, however, also possible for the production of the contact lens tobe carried out in a first cycle ("production cycle"), that is to say forthe piston-like mould member 11a to be moved upwards, for liquidstarting material to flow between the mould member 11a and the containerbase 100a and then for the mould member 11a to be moved downwards again.In the closed position the mould is then impinged upon by UV radiation3, as a result of which crosslinking occurs and the contact lens CL isthus produced. Then, in a separate second cycle ("flushing cycle"), thecontact lens can be flushed out of the mould without a new contact lensbeing produced in that second cycle, whereas in the "single-cycle"device a new contact lens CL is again produced. For the flushingoperation in the "two-cycle" device, it is therefore possible to useliquid starting material, but it is also possible, in particular, to usea separate cleaning liquid. This is of advantage in as much as the mouldcan be especially well cleaned on the inside during the flushing cyclebefore starting material flows in again in the next cycle and the nextcontact lens CL is produced. In the example embodiment according toFIGS. 3A-C, therefore, both a "single-cycle" operation (a contact lensis produced in every cycle) and a "two-cycle" operation (a contact lensis produced in the first cycle and in the second cycle it is flushed outand the mould cleaned without a new contact lens being produced) arepossible.

A further example embodiment of the device according to the invention isshown in FIGS. 4A-C. That example embodiment is in principle alsosimilar to the example embodiments described with reference to FIGS.2A-C and FIGS. 3A-C, but differs significantly from those in that itcomprises a somewhat differently constructed mould member 11bdisplaceable in the manner of a piston. In addition, the container 10bis also significantly differently constructed in the respect that thereis provided in one of its side walls 103b a hollow or recess 104b whichextends in the direction of movement of the piston-like mould member11b. Arranged in that recess 104b is a gripping device 4b. The mouldmember 11b has an indentation 114b on its outer wall 113b exactly in theregion in which the recess 104b is provided in the side wall 103b of thecontainer 11b. The mould member 11b furthermore comprises a channel 115bwhich can be connected to a negative pressure source and positivepressure source P3. The gripping device 4b can also be connected to thatnegative pressure and positive pressure source P3.

The manufacture of the contact lens CL by crosslinking by means ofimpingement of UV radiation 3 upon the mould is carried out in the samemanner as already described with reference to FIGS. 2A-C and FIGS. 3A-C.The explanation of FIGS. 4A-C is therefore directed mainly to the mannerin which the contact lens CL is removed from the mould. When the mouldis in the closed position, the mould is again impinged upon by UVradiation 3 and the contact lens CL is produced by crosslinking (FIG.4A). Starting material is then pumped by means of the pump P1 betweenthe mould member 11b and the container base 100b, and the mould member11b is moved upwards (FIG. 4B). The gripping device 4b is then pivotedout of the recess 104b and over the contact lens CL.

The gripping device 4b has a borehole in its gripper plate 40b throughwhich negative pressure is then applied by means of the negativepressure source P3, so that the contact lens CL is lifted and suckedtowards the gripper plate 40b. When the contact lens CL has been suckedagainst the gripper plate 40b, the gripping device 4b is pivoted backinto the recess 104b and the mould member 11b is moved downwards again.As that happens, the liquid starting material disposed between mouldmember 11b and container base 100b is sucked away by means of the pumpP2 (FIG. 4C).

The gripping device 4b disposed in the recess 104b at the same timeeither glides along the outer wall 113b of the mould member 11b or isheld in the recess 104b until the gripper plate 40b is located oppositethe indentation 114b on the outer wall of the mould member 11b. At thatpoint positive pressure is applied through the borehole in the gripperplate 40b, so that the contact lens CL is released from the gripperplate 40b and deposited in the indentation 114b. Negative pressure isapplied through the channel 115b leading to the indentation 114b at thesame time as the contact lens CL is released from the gripper plate 40b,so that the contact lens CL is simply deposited by the gripper plate 40bin the indentation 114b (FIG. 4A).

When the mould member 11b has been moved upwards, the indentation 114bof the mould member 11b is located outside the container 10b (FIG. 4B).If positive pressure is then applied through the channel 115b, thecontact lens CL is released from the indentation 114b and can beconveyed away for further processing. In this connection it should inparticular be noted that the side wall 103b can also be extended evenfurther upwards and can have a further recess in which the contact lensCL can be deposited or into which it can be flushed. By that means evenbetter guidance of the mould member 11b and preservation of itscorresponding sealing faces, which glide along the container wall, isachieved.

In FIGS. 4A-C the pump P3 is provided for the application of positivepressure or negative pressure, the positive pressure connection HP andnegative pressure connection NP of which pump are connected to thechannel 115b or the borehole in the gripper plate 40b depending on theposition of the mould member displaceable in the manner of a piston. Thepump P3 can suck starting material out of the reservoir R in which thestarting material is stored, by means of which the necessary pressure isgenerated. FIGS. 4A-C show at the inlet 101b and at the outlet 102b twoseparate reservoirs into which the pumps P1 or P2 and P3 respectivelyproject, but obviously it is also possible for there to be one reservoironly.

It should be noted at this point that also the example embodimentaccording to FIGS. 4A-C can operate both as a "single-cycle" device andas a "two-cycle" device. It must, however, be ensured in the case of the"single-cycle" device that it is always only starting material thatflows into the container 10b. In the "two-cycle" device, on the otherhand, in the second cycle in which the contact lens CL is also removed,a cleaning liquid can be fed in.

As already discussed in the explanation of the individual Figures, asthe mould halves are closed excess starting material is forced into theannular gap 16 between the two mould halves. The width or height (Δy) ofthe annular gap 16, which is shown more clearly in FIG. 5, is madesufficiently great for contact between the two mould halves 11 and 12(or contact between the mould member 11, 11a and 11b and the containerbase 100, 100a and 100b respectively) in the region of the mask 21 to beavoided with absolute reliability. The positioning (spacing) of the twomould halves is effected by the spacer bolts 19 (FIGS. 1A-C).

In FIG. 5, the mould cavity 15 has, by way of example, a shape thatcorresponds to the typical rim geometry of a so-called soft contactlens. The cavity rim, and thus the contact lens rim, is formed here by awall face 22 on the male mould half 12 and a wall face 23 on the femalemould half 11, the two wall faces being arranged at right angles to oneanother. The width and height of those two wall faces, that is to saythe rim areas of the contact lens defined by them, are indicated by Xand Y respectively. It is obviously also possible in practice for thelens rim to be somewhat rounded.

As can be seen clearly, the wall face 23 of the mould half 11 does notquite extend up to the wall face 22 but is lower by the amount Δy of theannular gap 16. Typical gap heights Δy are in the range below about 100μm for the manufacture of contact lenses. Tests have shown that, atleast when parallel energy radiation is used, a clean structuring of therim of the moulding being produced is still possible even with gapheights of approximately 1 mm. Conversely, however, the width or heightof the annular gap can also readily be reduced to practically zero,provided that the mould is closed without force, that is to say that thetwo mould halves lie one on top of the other without external pressure.In that case only a film of uncrosslinked material a few micrometersthick remains between the two mould halves in the region of the annulargap, which, however, because of the screening from the UV radiation,likewise cannot result in the formation of flash. On crosslinking,therefore, a clean and burr-free contact lens rim is formed that doesnot require any subsequent mechanical processing. On account of theforce-free closure of the mould, the mould is also not damaged, at leastif a suitable material has been chosen, and can thus be used repeatedly.

However, even if the mould is closed with the use of force, and wherenecessary used only once, the device according to the invention is stilldistinguished from the known devices by the fact that the mould isclosed in the starting material and can thus be closed more quicklywithout there being any risk of air inclusions.

When energy is applied from one side, the mould half remote from theenergy source can, in principle, be made from any material that iscompatible with the crosslinkable or cross-linked material or componentsthereof. If metals are used, however, depending on the nature of theenergy radiation the possibility of reflections must be expected, whichmay possibly result in undesired effects such as over-exposure, theformation of defects at the edges, or the like. Absorbent materials donot have those disadvantages.

In principle it is also possible to exploit in a controlled manner thediffraction and/or scattering effects of the radiation impinging uponthe mould in order to produce a moulding with a contour that isintentionally not sharp or has somewhat rounded edges. The same effectcan also be achieved using masks with locally variable permeability. Itis thus possible for sharp-edged rims of the moulding to be rounded in acontrolled manner by controlled incomplete crosslinking and by partialdissolution of the incompletely crosslinked regions with a suitablesolvent, which may also be the uncrosslinked starting material itself.Isopropanol, for example, is a suitable solvent when using HEMA(hydroxyethyl methacrylate) as the starting material.

Furthermore, it is clear that the device explained with reference to theFigures may also comprise several cavities instead of only one, so thatseveral contact lenses can be produced simultaneously in one cycle. Thatvariant is especially efficient.

In addition, in the variants with the piston-like mould member athroughflow control can be effected in a controlled manner to the effectthat first of all the piston-like mould member is acted upon by forcemechanically, and release of the starting material into the container asit is fed in is slightly delayed and release from the container as it isconveyed away is slightly delayed. This applies also to the variant inwhich both pumps are used and the piston is driven mechanically. Withthis measure it is possible for a reduced pressure when feeding in, anda raised pressure when conveying away, to be generated in the containerin a controlled manner, or for the pressure in the container to beinfluenced generally in that manner.

Also possible is a variant in which the number of cycles by which a newcontact lens is produced is variable. For example, a sensor can detectwhether a contact lens has actually been flushed out of the mould, andonly when the sensor has detected such a flushed-out contact lens is themould fully closed and a new contact lens produced. If the sensor hasnot detected a flushed-out contact lens, flushing of the mould iscontinued until the contact lens has been flushed out of the mould.

For contact lenses CL there may be used as starting material that can becrosslinked by irradiation with UV light, for example, the HEMA(hydroxyethyl methacrylate) or poly-HEMA used widely for such purposes,especially in admixture with a suitable crosslinker, such as, forexample, ethylene glycol dimethacrylate. For other mouldings, dependingon the intended use other material may possibly be used and, inprinciple, it is also possible for other forms of energy, for exampleelectron radiation, gamma radiation, thermal energy etc., to be used totrigger crosslinking depending on the nature of the crosslinkablematerial. In the manufacture of contact lenses, materials that arecrosslinkable by UV light are generally customary but not absolutelyessential.

Suitable starting materials are in particular special prepolymers,especially those based on polyvinyl alcohol, that comprise cyclic acetalgroups and crosslinkable groups.

Contact lenses based on polyvinyl alcohol are already known. Forexample, contact lenses comprising polyvinyl alcohol that has(meth)acryloyl groups bonded by way of urethane groups are disclosed,for example, in EP 216 074. Contact lenses made of polyvinyl alcoholcrosslinked with polyepoxides are described in EP 189 375.

Also already known are some special acetals that comprise crosslinkablegroups. Reference is made in that connection, for example, to EP 201693, EP 215 245 and EP 211 432. EP 201 693 describes, inter alia,acetals of unbranched aldehydes having from 2 to 11 carbon atoms thatcarry a terminal amino group which has been substituted by a C₃ -C₂₄-olefinically unsaturated organic radical. That organic radical has afunctionality which removes electrons from the nitrogen atom, and alsothe olefinically unsaturated functionality is polymerisable. Alsoclaimed in EP 201 693 are reaction products of the above-characterisedacetals with a 1,2-diol, a 1,3-diol, a polyvinyl alcohol or a cellulose.Products of that kind are not, however, expressly described.

Inasmuch as one of the acetals according to EP 201 693 is mentioned atall in connection with, for example, polyvinyl alcohol, as is the case,inter alia, in Example 17 of that Patent Application, then the acetalpolymerisable by way of its olefinic group is first copolymerised, forexample, with vinyl acetate. The copolymer so obtained is then reactedwith polyvinyl alcohol, and an emulsion with a pH of 5.43 and aviscosity of 11640 cps which contains 37% solids is obtained.

In contrast, according to one aspect of the present invention, theprepolymers comprise a 1,3-diol basic structure in which a certainpercentage of the 1,3-diol units have been modified to a 1,3-dioxanehaving in the 2-position a radical that is polymerisable but notpolymerised. The polymerisable radical is especially an aminoalkylradical having a polymerisable group bonded to the nitrogen atom.

The prepolymer according to the invention is preferably a derivative ofa polyvinyl alcohol having a molecular weight of at least about 2000that, based on the number of hydroxy groups of the polyvinyl alcohol,comprises from approximately 0.5 to approximately 80% of units offormula I ##STR1## wherein R is lower alkylene having up to 8 carbonatoms,

R¹ is hydrogen or lower alkyl and

R² is an olefinically unsaturated, electron-attracting, copolymerisableradical preferably having up to 25 carbon atoms.

R² is, for example, an olefinically unsaturated acyl radical of formulaR³ --CO--, in which

R³ is an olefinically unsaturated copolymerisable radical having from 2to 24 carbon atoms, preferably from 2 to 8 carbon atoms, especiallypreferably from 2 to 4 carbon atoms. In another embodiment, the radicalR² is a radical of formula II

    --CO--NH--(R.sup.4 --NH--CO--O).sub.q --R.sup.5 --O--CO--R.sup.3(II)

wherein

q is zero or one and

R⁴ and R⁵ are each independently lower alkylene having from 2 to 8carbon atoms, arylene having from 6 to 12 carbon atoms, a saturateddivalent cycloaliphatic group having from 6 to 10 carbon atoms,arylenealkylene or alkylenearylene having from 7 to 14 carbon atoms orarylenealkylenearylene having from 13 to 16 carbon atoms, and

R³ is as defined above.

The prepolymer according to the invention is therefore especially aderivative of a polyvinyl alcohol having a molecular weight of at leastabout 2000 that, based on the number of hydroxy groups of the polyvinylalcohol, comprises from approximately 0.5 to approximately 80% of unitsof formula III ##STR2## wherein R is lower alkylene,

R¹ is hydrogen or lower alkyl,

p is zero or one,

q is zero or one,

R³ is an olefinically unsaturated copolymerisable radical having from 2to 8 carbon atoms and

R⁴ and R⁵ are each independently lower alkylene having from 2 to 8carbon atoms, arylene having from 6 to 12 carbon atoms, a saturateddivalent cycloaliphatic group having from 6 to 10 carbon atoms,arylenealkylene or alkylenearylene having from 7 to 14 carbon atoms orarylenealkylenearylene having from 13 to 16 carbon atoms.

Lower alkylene R preferably has up to 8 carbon atoms and may bestraight-chained or branched. Suitable examples include octylene,hexylene, pentylene, butylene, propylene, ethylene, methylene,2-propylene, 2-butylene or 3-pentylene. Preferably lower alkylene R hasup to 6 and especially preferably up to 4 carbon atoms. The meaningsmethylene and butylene are especially preferred.

R¹ is preferably hydrogen or lower alkyl having up to seven, especiallyup to four, carbon atoms, especially hydrogen.

Lower alkylene R⁴ or R⁵ preferably has from 2 to 6 carbon atoms and isespecially straight-chained. Suitable examples include propylene,butylene, hexylene, dimethylethylene and, especially preferably,ethylene.

Arylene R⁴ or R⁵ is preferably phenylene that is unsubstituted or issubstituted by lower alkyl or lower alkoxy, especially 1,3-phenylene or1,4-phenylene or methyl-1,4-phenylene.

A saturated divalent cycloaliphatic group R⁴ or R⁵ is preferablycyclohexylene or cyclohexylene-lower alkylene, for examplecyclohexylenemethylene, that is unsubstituted or is substituted by oneor more methyl groups, such as, for example,trimethylcyclohexylenemethylene, for example the divalent isophoroneradical.

The arylene unit of alkylenearylene or arylenealkylene R⁴ or R⁵ ispreferably phenylene, unsubstituted or substituted by lower alkyl orlower alkoxy, and the alkylene unit thereof is preferably loweralkylene, such as methylene or ethylene, especially methylene. Suchradicals R⁴ or R⁵ are therefore preferably phenylenemethylene ormethylenephenylene.

Arylenealkylenearylene R⁴ or R⁵ is preferably phenylene-loweralkylene-phenylene having up to 4 carbon atoms in the alkylene unit, forexample phenyleneethylenephenylene.

The radicals R⁴ and R⁵ are each independently preferably lower alkylenehaving from 2 to 6 carbon atoms, phenylene, unsubstituted or substitutedby lower alkyl, cyclohexylene or cyclohexylene-lower alkylene,unsubstituted or substituted by lower alkyl, phenylene-lower alkylene,lower alkylene-phenylene or phenylene-lower alkylene-phenylene.

Within the scope of this invention, the term "lower" used in connectionwith radicals and compounds denotes radicals or compounds having up to 7carbon atoms, preferably up to 4 carbon atoms, unless defined otherwise.

Lower alkyl has especially up to 7 carbon atoms, preferably up to 4carbon atoms, and is, for example, methyl, ethyl, propyl, butyl ortert-butyl.

Lower alkoxy has especially up to 7 carbon atoms, preferably up to 4carbon atoms, and is, for example, methoxy, ethoxy, propoxy, butoxy ortert-butoxy.

The olefinically unsaturated copolymerisable radical R³ having from 2 to24 carbon atoms is preferably alkenyl having from 2 to 24 carbon atoms,especially alkenyl having from 2 to 8 carbon atoms and especiallypreferably alkenyl having from 2 to 4 carbon atoms, for example ethenyl,2-propenyl, 3-propenyl, 2-butenyl, hexenyl, octenyl or dodecenyl. Themeanings ethenyl and 2-propenyl are preferred, so that the group--CO--R³ is the acyl radical of acrylic or methacrylic acid.

The divalent group --R⁴ --NH--CO--O-- is present when q is one andabsent when q is zero. Prepolymers in which q is zero are preferred.

The divalent group --CO--NH--(R⁴ --NH--CO--O)_(q) --R⁵ --O-- is presentwhen p is one and absent when p is zero. Prepolymers in which p is zeroare preferred.

In prepolymers in which p is one the index q is preferably zero.Prepolymers in which p is one, the index q is zero and R⁵ is loweralkylene are especially preferred.

A preferred prepolymer according to the invention is thereforeespecially a derivative of a polyvinyl alcohol having a molecular weightof at least about 2000 that, based on the number of hydroxy groups ofthe polyvinyl alcohol, comprises from approximately 0.5 to approximately80% of units of formula III in which R is lower alkylene having up to 6carbon atoms, p is zero and R³ is alkenyl having from 2 to 8 carbonatoms.

A further preferred prepolymer according to the invention is thereforeespecially a derivative of a polyvinyl alcohol having a molecular weightof at least about 2000 that, based on the number of hydroxy groups ofthe polyvinyl alcohol, comprises from approximately 0.5 to approximately80% of units of formula III in which R is lower alkylene having up to 6carbon atoms, p is one, q is zero, R⁵ is lower alkylene having from 2 to6 carbon atoms and R³ is alkenyl having from 2 to 8 carbon atoms.

A further preferred prepolymer according to the invention is thereforeespecially a derivative of a polyvinyl alcohol having a molecular weightof at least about 2000 that, based on the number of hydroxy groups ofthe polyvinyl alcohol, comprises from approximately 0.5 to approximately80% of units of formula III in which R is lower alkylene having up to 6carbon atoms, p is one, q is one, R⁴ is lower alkylene having from 2 to6 carbon atoms, phenylene, unsubstituted or substituted by lower alkyl,cyclohexylene or cyclohexylene-lower alkylene, unsubstituted orsubstituted by lower alkyl, phenylene-lower alkylene, loweralkylene-phenylene or phenylene-lower alkylene-phenylene, R⁵ is loweralkylene having from 2 to 6 carbon atoms and R³ is alkenyl having from 2to 8 carbon atoms.

The prepolymers according to the invention are derivatives of polyvinylalcohol having a molecular weight of at least about 2000 that, based onthe number of hydroxy groups of the polyvinyl alcohol, comprises fromapproximately 0.5 to approximately 80%, especially approximately from 1to 50%, preferably approximately from 1 to 25%, preferably approximatelyfrom 2 to 15% and especially preferably approximately from 3 to 10%, ofunits of formula III. Prepolymers according to the invention which areprovided for the manufacture of contact lenses comprise, based on thenumber of hydroxy groups of the polyvinyl alcohol, especially fromapproximately 0.5 to approximately 25%, especially approximately from 1to 15% and especially preferably approximately from 2 to 12%, of unitsof formula III.

Polyvinyl alcohols that can be derivatised in accordance with theinvention preferably have a molecular weight of at least 10,000. As anupper limit the polyvinyl alcohols may have a molecular weight of up to1,000,000. Preferably, the polyvinyl alcohols have a molecular weight ofup to 300,000, especially up to approximately 100,000 and especiallypreferably up to approximately 50,000.

Polyvinyl alcohols suitable in accordance with the invention usuallyhave a poly(2-hydroxy)ethylene structure. The polyvinyl alcoholsderivatised in accordance with the invention may, however, also comprisehydroxy groups in the form of 1,2-glycols, such as copolymer units of1,2-dihydroxyethylene, as may be obtained, for example, by the alkalinehydrolysis of vinyl acetate/vinylene carbonate copolymers.

In addition, the polyvinyl alcohols derivatised in accordance with theinvention may also comprise small proportions, for example up to 20%,preferably up to 5%, of copolymer units of ethylene, propylene,acrylamide, methacrylamide, dimethacrylamide, hydroxyethyl methacrylate,methyl methacrylate, methyl acrylate, ethyl acrylate, vinylpyrrolidone,hydroxyethyl acrylate, allyl alcohol, styrene or similar customarilyused comonomers.

Commercially available polyvinyl alcohols may be used, such as, forexample, Vinol® 107 produced by Air Products (MW=22,000 to 31,000,98-98.8% hydrolysed), Polysciences 4397 (MW=25,000, 98.5% hydrolysed),BF 14 produced by Chan Chun, Elvanol® 90-50 produced by DuPont, UF-120produced by Unitika, Moviol® 4-88, 10-98 and 20-98 produced by Hoechst.Other manufacturers are, for example, Nippon Gohsei (Gohsenol®),Monsanto (Gelvatol®), Wacker (Polyviol®) and the Japanese manufacturersKuraray, Denki and Shin-Etsu.

As already mentioned, it is also possible to use copolymers ofhydrolysed vinyl acetate, which are obtainable, for example, in the formof hydrolysed ethylene/vinyl acetate (EVA), or vinyl chloride/vinylacetate, N-vinylpyrrolidone/vinyl acetate and maleic acidanhydride/vinyl acetate.

Polyvinyl alcohol is usually prepared by hydrolysis of the correspondinghomopolymeric polyvinyl acetate. In a preferred embodiment, thepolyvinyl alcohol derivatised in accordance with the invention comprisesless than 50% of polyvinyl acetate units, especially less than 20% ofpolyvinyl acetate units.

The compounds comprising units of formula III may be prepared in amanner known per se. For example, a polyvinyl alcohol having a molecularweight of at least about 2000 that comprises units of formula IV

    --CH(OH)--CH.sub.2 --                                      (IV)

may be reacted with approximately from 0.5 to 80%, based on the numberof hydroxy groups of the compound of formula IV, of a compound offormula (V) ##STR3## in which R' and R" are each independently hydrogen,lower alkyl or lower alkanoyl, such as acetyl or propionyl, and theother variables are as defined for formula III, especially in an acidicmedium.

Alternatively, a polyvinyl alcohol having a molecular weight of at leastabout 2000 that comprises units of formula IV may be reacted with acompound of formula VI ##STR4## in which the variables are as definedfor the compound of formula V, especially under acidic conditions, andthe cyclic acetal obtainable in that manner may then be reacted with acompound of formula VII

    OCN--(R.sup.4 --NH--CO--O).sub.q --R.sup.5 --O--CO--R.sup.3(VII)

in which the variables are as defined for the compound of formula V.

Alternatively, the reaction product of a compound of formula IV and acompound of formula VI may be reacted, similarly to the productobtainable as described above, with a compound of formula (VIII)

    X--CO--R.sup.3                                             (VIII)

in which R³ is, for example, alkenyl having from 2 to 8 carbon atoms andX is a reactive group, for example etherified or esterified hydroxy, forexample halogen, especially chlorine.

Compounds of formula V in which p is zero are known, for example, fromEP 201 693. Compounds of formula VI are also described therein.Compounds of formula VII are known per se, or can be prepared in amanner known per se. An example of a compound of formula VII in which qis zero is isocyanatoethyl methacrylate. An example of a compound offormula VII in which q is one is the reaction product of isophoronediisocyanate with 0.5 equivalent of hydroxyethyl methacrylate. Compoundsof formula VIII are known per se; a typical representative ismethacryloyl chloride. Compounds of formula V in which p and/or q are 1can be prepared in a manner known per se from the above-mentionedcompounds, for example by reaction of a compound of formula VI withisocyanatoethyl methacrylate or by reaction of a compound of formula VIwith isophorone diisocyanate which has previously been terminated with0.5 equivalent of hydroxyethyl methacrylate.

Surprisingly the prepolymers of formulae I and III are extraordinarilystable. This is unexpected for the person skilled in the art because,for example, higher-functional acrylates usually have to be stabilised.If such compounds are not stabilised then rapid polymerisation usuallyoccurs. Spontaneous crosslinking by homopolymerisation does not occur,however, with the prepolymers of the invention. The prepolymers offormulae I and III can furthermore be purified in a manner known per se,for example by precipitation with acetone, dialysis or ultrafiltration,ultrafiltration being especially preferred. By means of thatpurification process the prepolymers of formulae I and III can beobtained in extremely pure form, for example in the form of concentratedaqueous solutions that are free, or at least substantially free, fromreaction products, such as salts, and starting materials, such as, forexample, compounds of formula V or other non-polymeric constituents.

The preferred purification process for the prepolymers of the invention,ultrafiltration, can be carried out in a manner known per se. It ispossible for the ultrafiltration to be carried out repeatedly, forexample from two to ten times. Alternatively, the ultrafiltration can becarried out continuously until the selected degree of purity isattained. The selected degree of purity can in principle be as high asdesired. A suitable measure for the degree of purity is, for example,the sodium chloride content of the solution, which can be determinedsimply in known manner.

The prepolymers of formulae I and III according to the invention are onthe other hand crosslinkable in an extremely effective and controlledmanner, especially by photocrosslinking.

In the case of photocrosslinking, appropriately a photoinitiator isadded which can initiate radical crosslinking. Examples thereof arefamiliar to the person skilled in the art and suitable photoinitiatorsthat may be mentioned specifically are benzoin methyl ether,1-hydroxycyclohexylphenyl ketone, Daracure 1173 or Irgacure types. Thecrosslinking can then be triggered by actinic radiation, such as, forexample, UV light, or ionising radiation, such as, for example, gammaradiation or X-radiation.

The photopolymerisation is suitably carried out in a solvent. A suitablesolvent is in principle any solvent that dissolves polyvinyl alcohol andthe vinylic comonomers optionally used in addition, for example water,alcohols, such as lower alkanols, for example ethanol or methanol, alsocarboxylic acid amides, such as dimethylformamide, or dimethylsulfoxide, and also a mixture of suitable solvents, such as, forexample, a mixture of water with an alcohol, such as, for example, awater/ethanol or a water/methanol mixture.

The photocrosslinking is carried out preferably directly from an aqueoussolution of the prepolymers according to the invention, which can beobtained by the preferred purification step, ultrafiltration, whereappropriate after the addition of an additional vinylic comonomer. Forexample, an approximately 15 to 40% aqueous solution can bephotocrosslinked.

The process for the preparation of the polymers of the invention maycomprise, for example, photocrosslinking a prepolymer comprising unitsof formula I or III, especially in substantially pure form, that is tosay, for example, after single or repeated ultra-filtration, preferablyin solution, especially in aqueous solution, in the absence or presenceof an additional vinylic comonomer.

The vinylic comonomer which, in accordance with the invention, may beused in addition in the photocrosslinking, may be hydrophilic orhydrophobic, or a mixture of a hydrophobic and a hydrophilic vinylicmonomer. Suitable vinylic monomers include especially those customarilyused in the manufacture of contact lenses. A hydrophilic vinylic monomerdenotes a monomer that typically yields as homopolymer a polymer that iswater-soluble or can absorb at least 10% by weight of water.Analogously, a hydrophobic vinylic monomer denotes a monomer thattypically yields as homopolymer a polymer that is water-insoluble andcan absorb less than 10% by weight of water.

Generally, approximately from 0.01 to 80 units of a typical vinyliccomonomer react per unit of formula I or III.

If a vinylic comonomer is used, the crosslinked polymers according tothe invention preferably comprise approximately from 1 to 15%,especially preferably approximately from 3 to 8%, of units of formula Ior III, based on the number of hydroxy groups of the polyvinyl alcohol,which are reacted with approximately from 0.1 to 80 units of the vinylicmonomer.

The proportion of the vinylic comonomers, if used, is preferably from0.5 to 80 units per unit of formula I, especially from 1 to 30 units perunit of formula I, and especially preferably from 5 to 20 units per unitof formula I.

It is also preferable to use a hydrophobic vinylic comonomer or amixture of a hydrophobic vinylic comonomer with a hydrophilic vinyliccomonomer, the mixture comprising at least 50% by weight of ahydrophobic vinylic comonomer. In that manner the mechanical propertiesof the polymer can be improved without the water content fallingsubstantially. In principle, however, both conventional hydrophobicvinylic comonomers and conventional hydrophilic vinylic comonomers aresuitable for the copolymerisation with polyvinyl alcohol comprisinggroups of formula I.

Suitable hydrophobic vinylic comonomers include, without the list beingexhaustive, C₁ -C₁₈ alkyl acrylates and methacrylates, C₃ -C₁₈ alkylacrylamides and methacrylamides, acrylonitrile, methacrylonitrile,vinyl-C₁ -C₁₈ alkanoates, C₂ -C₁₈ alkenes, C₂ -C₁₈ haloalkenes, styrene,C₁ -C₆ alkylstyrene, vinyl alkyl ethers, in which the alkyl moietycontains from 1 to 6 carbon atoms, C₂ -C₁₀ perfluoroalkyl acrylates andmethacrylates or correspondingly partially fluorinated acrylates andmethacrylates, C₃ -C₁₂ perfluoroalkyl-ethylthiocarbonylaminoethylacrylates and methacrylates, acryloxy- and methacryloxy-alkylsiloxanes,N-vinylcarbazole, C₁ -C₁₂ alkyl esters of maleic acid, fumaric acid,itaconic acid, mesaconic acid and the like. C₁ -C₄ alkyl esters ofvinylically unsaturated carboxylic acids having from 3 to 5 carbon atomsor vinyl esters of carboxylic acids having up to 5 carbon atoms, forexample, are preferred.

Examples of suitable hydrophobic vinylic comonomers include methylacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate,cyclohexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethylmethacrylate, propyl methacrylate, vinyl acetate, vinyl propionate,vinyl butyrate, vinyl valerate, styrene, chloroprene, vinyl chloride,vinylidene chloride, acrylonitrile, 1-butene, butadiene,methacrylonitrile, vinyltoluene, vinyl ethyl ether,perfluorohexylethylthiocarbonylaminoethyl methacrylate, isobornylmethacrylate, trifluoroethyl methacrylate, hexafluoroisopropylmethacrylate, hexafluorobutyl methacrylate,tris-trimethylsilyloxy-silyl-propyl methacrylate,3-methacryloxypropylpentamethyldisiloxane andbis(methacryloxypropyl)tetramethyldisiloxane.

Suitable hydrophilic vinylic comonomers include, without the list beingexhaustive, hydroxy-substituted lower alkyl acrylates and methacrylates,acrylamide, methacrylamide, lower alkyl acrylamides and methacrylamides,ethoxylated acrylates and methacrylates, hydroxy-substituted lower alkylacrylamides and methacrylamides, hydroxy-substituted lower alkyl vinylethers, sodium ethylenesulfonate, sodium styrenesulfonate,2-acrylamido-2-methylpropanesulfonic acid, N-vinylpyrrole,N-vinylsuccinimide, N-vinylpyrrolidone, 2- or 4-vinylpyridine, acrylicacid, methacrylic acid, amino- (the term "amino" also includingquaternary ammonium), mono-lower alkylamino- or di-loweralkylamino-lower alkyl acrylates and methacrylates, allyl alcohol andthe like. Hydroxy-substituted C₂ -C₄ alkyl(meth)acrylates, five- toseven-membered N-vinyl lactams, N,N-di-C₁ -C₄ alkyl(meth)acrylamides andvinylically unsaturated carboxylic acids having a total of from 3 to 5carbon atoms, for example, are preferred.

Examples of suitable hydrophilic vinylic comonomers include hydroxyethylmethacrylate, hydroxyethyl acrylate, acrylamide, methacrylamide,dimethylacrylamide, allyl alcohol, vinylpyridine, vinylpyrrolidone,glycerol methacrylate, N-(1,1-dimethyl-3-oxobutyl)acrylamide, and thelike.

Preferred hydrophobic vinylic comonomers are methyl methacrylate andvinyl acetate.

Preferred hydrophilic vinylic comonomers are 2-hydroxyethylmethacrylate, N-vinylpyrrolidone and acrylamide.

EXAMPLES

In the following Examples, unless expressly stated otherwise amounts areamounts by weight, and temperatures are in degrees Celsius. The Examplesare not intended to limit the invention in any way, for instance to thescope of the Examples.

Example 1a)

Over a period of 4 hours, 104.5 parts of methacryloyl chloride dissolvedin 105 parts of dichloromethane are added dropwise at a maximum of 15°C., while cooling with ice, to 105.14 parts of aminoacetaldehydedimethylacetal and 101.2 parts of triethylamine in 200 parts ofdichloromethane. When the reaction is complete, the dichloromethanephase is washed with 200 parts of water then with 200 parts of 1N HClsolution, and then twice with 200 parts of water. After drying withanhydrous magnesium sulfate, the dichloromethane phase is concentratedby evaporation and stabilised with 0.1% of 2,6-di-tert-butyl-p-cresol,based on the reaction product. After distillation at 90° C./10⁻³ mbar,112 g of methacrylamidoacetaldehyde dimethylacetal are obtained in theform of a colourless liquid, boiling point 92° C./10⁻³ mbar (65% yield).

Example 1b)

52.6 g of aminoacetaldehyde dimethylacetal are dissolved in 150 ml ofdeionised water and cooled to 5° C. with ice. Subsequently, 50 ml ofmethacrylic acid chloride and 50 ml of 30% sodium hydroxide solution aresimultaneously so added over a period of 40 minutes that the pH valueremains at 10 and the temperature does not exceed 20° C. When theaddition is complete, the remaining content of aminoacetaldehydedimethylacetal is determined as 0.18% by gas chromatography. The amineis reacted fully by the further addition of 2.2 ml of methacrylic acidchloride and 2.0 ml of 30% sodium hydroxide solution. The solution isthen neutralised with 1N hydrochloric acid (pH=7). The aqueous phase isextracted with 50 ml of petroleum ether and washed with water. Thepetroleum ether phase contains 3.4 g of secondary product. The aqueousphases are combined and yield 402.8 g of a 20.6% solution ofmethacrylamidoacetaldehyde dimethylacetal. According to a gaschromatogram, the product is 98.2%.

Example 2

10 parts of polyvinyl alcohol having a molecular weight of 22,000 and adegree of hydrolysis of 97.5-99.5% are dissolved in 90 parts of water,2.5 parts of methacrylamidoacetaldehyde dimethylacetal are added and themixture is acidified with 10 parts of concentrated hydrochloric acid.The solution is stabilised with 0.02 parts of2,6-di-tert-butyl-p-cresol. After stirring for 20 hours at roomtemperature, the solution is adjusted to pH 7 with 10% sodium hydroxidesolution and then ultrafiltered seven times using a 3 kD membrane (ratio1:3). After concentration, an 18.8% aqueous solution ofmethacrylamidoacetaldehydo-1,3-acetal of polyvinyl alcohol having aviscosity of 2240 cP at 25° C. is obtained.

Example 3

10 parts of the solution of methacrylamidoacetaldehydo-1,3-acetal ofpolyvinyl alcohol obtained in accordance with Example 2 arephotochemically crosslinked by adding 0.034 parts of Darocure 1173(CIBA-GEIGY) thereto. The mixture is irradiated in the form of a 100micron thick layer between two glass plates with 200 pulses of a 5000watt irradiation device produced by Staub. A solid transparent film witha solids content of 31% is obtained.

Example 4

110 g of polyvinyl alcohol (Moviol 4-88, Hoechst) are dissolved at 90°C. in 440 g of deionised water and cooled to 22° C. 100.15 g of a 20.6%aqueous solution of methacrylamidoacetaldehyde dimethylacetal, 38.5 g ofconcentrated hydrochloric acid (37% p.a., Merck) and 44.7 g of deionisedwater are added thereto. The mixture is stirred at room temperature for22 hours and then adjusted to pH 7.0 with a 5% NaOH solution. Thesolution is diluted to 3 liters with deionised water, filtered andultrafiltered using a 1-KD-Omega membrane produced by Filtron. After thethree-fold specimen volume has permeated, the solution is concentrated.660 g of a 17.9% solution of the methacrylamidoacetaldehydo-1,3-acetalof polyvinyl alcohol having a viscosity of 210 cp are obtained. Theinherent viscosity of the polymer is 0.319. The nitrogen content is0.96%. According to NMR investigation, 11 mol % of the OH groups havebeen acetalised and 5 mol % of the OH groups acetylated. Concentrationof the aqueous polymer solution under reduced pressure and with airdraft yields a 30.8% solution having a viscosity of 3699 cp.

Example 5

66.6 g of deionised water, 3.3 g of monomeric4-methacrylamidobutyraldehyde diethylacetal and 20.0 g of concentratedhydrochloric acid (37% p.a., Merck) are added to 133.3 g of a 15%polyvinyl alcohol solution (Moviol 4-88, Hoechst) and the mixture isstirred at room temperature for 8 hours. The solution is then adjustedto pH 7 with 5% sodium hydroxide solution. After ultrafiltration of thesolution using a 3-KD-Omega membrane produced by Filtron, the sodiumchloride content of the polymer solution being reduced from 2.07% to0.04%, a 20% polymer solution of themethacrylamidobutyraldehydo-1,3-acetal of polyvinyl alcohol having aviscosity of 400 cp is obtained. The inherent viscosity of the polymeris 0.332. The nitrogen content is 0.41%. According to NMR investigation,7.5 mol % of the OH groups are charged with acetal groups and 7.3 mol %of the OH groups are charged with acetate groups.

Example 6

2.4 g (14.8 mmol) of aminobutyraldehyde diethylacetal (Fluka) and 20 gof concentrated hydrochloric acid (37% p.a., Merck) are added to 200 gof a 10% polyvinyl alcohol solution (Moviol 4-88, Hoechst). The solutionis stirred at room temperature for 48 hours and then neutralised with10% sodium hydroxide solution. The solution is diluted to 400 ml. 200 mlof the solution are further processed in accordance with Example 7. 0.85g (8.1 mmol) of methacrylic acid chloride (Fluka) is added to theremaining 200 ml of the solution and the pH value is maintained at 10with 2N sodium hydroxide solution. After 30 minutes at room temperature,the pH is adjusted to 7.0 and the solution is purified analogously toExample 5 using a 3-KD-Omega membrane produced by Filtron. Concentrationyields a 27.6% polymer solution of themethacrylamidobutyraldehydo-1,3-acetal of polyvinyl alcohol having aviscosity of 2920 cp. The inherent viscosity of the polymer is 0.435.The nitrogen content is 0.59%.

Example 7

1.3 g (8.5 mmol) of 2-isocyanatoethyl methacrylate are added to 200 mlof the polymer solution of Example 6 and the pH maintained at 10 with 2Nsodium hydroxide solution. After 15 minutes at room temperature thesolution is neutralised with 2N hydrochloric acid and ultrafilteredanalogously to Example 6. Concentration yields a 27.1% polymer solutionof the 4-(2-methacryloylethyl-ureido)butyraldehydo-1,3-acetal ofpolyvinyl alcohol having a viscosity of 2320 cp. The inherent viscosityof the polymer is 0.390. The nitrogen content is 1.9%.

Example 8

0.7% Darocur 1173 (based on the content of polymer) is added to the30.8% polymer solution according to Example 4 having a viscosity ofapproximately 3600 cp. The solution is introduced into a transparentcontact lens mould of polypropylene and the mould is closed. Thesolution is irradiated for 6 seconds from a distance of 18 cm using a200 watt Oriel UV lamp. The mould is opened and the finished contactlens can be removed. The contact lens is transparent and has a watercontent of 61%. The modulus is 0.9 mPa, the flexural elongation (DIN 53371) 50%. The contact lens is autoclaved for 40 minutes at 121° C. Nochanges in shape can be detected in a contact lens treated in thatmanner.

Example 9

0.0268 g of Darocur 1173 (0.7% based on the polymer content) and 0.922 gof methyl methacrylate are added to 10.00 g of a 27.1% polymer solutionaccording to Example 7. After the addition of 2.3 g of methanol a clearsolution is obtained. That solution is irradiated for a period of 14seconds analogously to Example 8, using a 200 watt Oriel lamp. Atransparent contact lens having a water content of 70.4% is obtained.

Example 10

1.04 g of acrylamide and 0.03 g of Darocur 1173 are added to 12.82 g ofa 24.16% solution of the prepolymer of Example 4. The clear solution isthen irradiated for 14 seconds analogously to Example 8, using a 200watt Oriel lamp. A contact lens having a water content of 64.4% isobtained.

The polymers according to the invention can be processed in a mannerknown per se into mouldings, especially contact lenses, for example bycarrying out the photocrosslinking of the prepolymers according to theinvention in contact lens moulds in the manner described in detailfurther above. Further examples of mouldings according to the invention,besides contact lenses, are biomedicinal or especially ophthalmicmouldings, for example intraocular lenses, eye bandages, mouldings thatcan be used in surgery, such as heart valves, artificial arteries or thelike, and also films or membranes, for example membranes for diffusioncontrol, photostructurizable films for information storage, orphotoresist materials, for example membranes or mouldings for etchresist or screen printing resist.

Contact lenses that comprise a polymer according to the invention asdescribed above or consist substantially or wholly of such a polymerhave a wide range of unusual and extremely advantageous properties,which include, for example, their excellent compatibility with the humancornea, which is based on a balanced relationship of water content,oxygen permeability and mechanical properties. The contact lensesaccording to the invention furthermore exhibit a high degree ofdimensional stability. No changes in shape are detected even afterautoclaving at, for example, about 120° C.

Attention may also be drawn to the fact that such contact lenses can, asdescribed, be produced in a very simple and efficient manner comparedwith the state of the art. This is as a result of several factors.First, the starting materials can be obtained or produced at afavourable cost. Secondly, there is the advantage that the prepolymersare surprisingly stable, so that they can be subjected to a high degreeof purification. It is therefore possible to use for the crosslinking amaterial that requires practically no subsequent purification, such asespecially a complicated extraction of unpolymerised constituents.

Also, the polymerisation can be carried out in aqueous solution, so thata subsequent hydration step is not necessary. Finally, thephotopolymerisation occurs within a short period, so that the processfor manufacturing the contact lenses according to the invention can beorganised to be extremely economical from that point of view also.

All of the advantages mentioned above naturally apply not only tocontact lenses but also to other mouldings according to the invention.Taking into account all the various advantageous aspects in themanufacture of the mouldings according to the invention it can be seenthat the mouldings according to the invention are especially suitable asmass-produced articles, such as, for example, contact lenses that areworn for a short time and then replaced by new lenses.

What is claimed is:
 1. A process for the manufacture of mouldings from astarting material that is crosslinkable by the impingement of suitableenergy in a mould, wherein the mould is at least partially permeable tothe energy and comprises two mould halves, each of the mould halveshaving a shape-forming surface and the shape-forming surfaces of the twomould halves forming a mould cavity, the process comprising the stepsof:(a) filling the mould cavity with the starting material in a still atleast partially uncrosslinked state, and (b) impinging the crosslinkingenergy to crosslink the starting material in the mould cavity to form amoulding,wherein the filling of the mould cavity is carried out whilethe shape-forming surfaces are immersed in the starting material suchthat the shape-forming surfaces of the mould cavity are continuouslyimmersed in the starting material during the filling and impingingsteps.
 2. A process according to claim 1, wherein for filling the mouldcavity the cavity is connected to a reservoir which surrounds it, inwhich the starting material is stored and from which the mould cavity isflooded.
 3. A process according to claim 1, wherein the mould isimmersed in the starting material.
 4. A process according to claim 1,wherein a mould is used that comprises a container and a mould memberthat is displaceable in that container and can be moved away from andtowards the container wall lying opposite it for the purpose of openingand closing the mould, starting material being fed in between thecontainer wall and the mould member as the mould is opened and conveyedaway again as the mould is closed.
 5. A process according to claim 4,wherein the container wall has one of the shape-forming surfaces and thedisplaceable mould member has the other shape-forming surface.
 6. Aprocess according to claim 4, wherein pumps are used to feed in andconvey away the starting material.
 7. A process according to claim 4,wherein the displaceable mould member is driven in order to feed in andconvey away the starting material.
 8. A process according to claim 1,wherein the moulding is capable of being released from the mould byflushing out the mould with starting material.
 9. A process according toclaim 4, wherein the moulding is separated from the mould by the flow ofstarting material as the mould is opened and is flushed out of the mouldby the flow of starting material as the mould is closed.
 10. A processaccording to claim 8, wherein in a first cycle, the mould is opened andclosed, then the crosslinking energy is impinged, and, in a secondcycle, the mould is opened again, the moulding being separated form themould and the mould member then being moved back towards theopposite-lying container wall in order to close the mould, in the courseof which the moulding is flushed out of the mould.
 11. A processaccording to claim 1, wherein the moulding is removed from the mould bymeans of a gripping device.
 12. A process according to claim 4, whereinthe moulding removed from the mould by the gripping device is depositedon the displaceable mould member outside the space between thedisplaceable mould member and the opposite-lying container wall.
 13. Aprocess according to claim 12, wherein the moulding deposited on thedisplaceable mould member is held fast thereto by negative pressure andthen released from it by positive pressure.
 14. A process according toclaim 1, wherein the mould is not fully closed after the introduction ofthe starting material into the mould cavity, so that an annular gapcontaining uncrosslinked starting material remains open, which gapsurrounds the mould cavity and is in communication with that mouldcavity.
 15. A process according to claim 14, wherein the mould is closedfurther following crosslinking shrinkage as crosslinking of the materialprogresses.
 16. A process according to claim 15, wherein a startingmaterial that is of at least viscous flowability prior to thecrosslinking is used, and wherein starting material can flow backthrough the annular gap into the mould cavity to compensate forshrinkage.
 17. A process according to claim 1, wherein the startingmaterial is a prepolymer that is a derivative of a polyvinyl alcoholhaving a molecular weight of at least about 2000 that, based on thenumber of hydroxy groups of the polyvinyl alcohol, comprises fromapproximately 0.5 to approximately 80% of units of ##STR5## wherein R islower alkylene having up to 8 carbon atoms,R¹ is hydrogen or lower alkyland R² is an olefinically unsaturated, electron-attracting,copolymerisable radical having up to 25 carbon atoms.
 18. A processaccording to claim 17, wherein the starting material is a prepolymerwherein R² is an olefinically unsaturated acyl radical of the formula R³--CO--, in which R³ is an olefinically unsaturated copolymerisableradical having from 2 to 24 carbon atoms.
 19. A process according toclaim 18, wherein the starting material is a prepolymer wherein R³ isalkenyl having from 2 to 8 carbon atoms.
 20. A process according toclaim 17, wherein the starting material is a prepolymer wherein theradical R² is a radical of formula II

    --CO--NH--(R.sup.4 --NH--CO--O).sub.q --R.sup.5 --O--CO--R.sup.3(II)

wherein q is zero or one and R⁴ and R⁵ are each independently loweralkylene having from 2 to 8 carbon atoms, arylene having from 6 to 12carbon atoms, a saturated divalent cycloaliphatic group having from 6 to10 carbon atoms, arylenealkylenearylene having from 13 to 16 carbonatoms, and R³ is an olefinically unsaturated copolymerisable radicalhaving from 2 to 24 carbon atoms.
 21. A process according to claim 17wherein the starting material is a derivative of a polyvinyl alcoholhaving a molecular weight of at least about 2000 that, based on thenumber of hydroxy groups of the polyvinyl alcohol, comprises fromapproximately 0.5 to approximately 80% of units of formula III ##STR6##wherein R is lower alkylene,R¹ is hydrogen or lower alkyl, p is zero orone, q is zero or one, R³ is an olefinically unsaturated copolymerisableradical having from 2 to 8 carbon atoms and R⁴ and R⁵ are eachindependently lower alkylene having from 2 to 8 carbon atoms, arylenehaving from 6 to 12 carbon atoms, a saturated divalent cycloaliphaticgroup having from 6 to 10 carbon atoms, arylenealkylene oralkylenearylene having from 7 to 14 carbon atoms orarylenealkylenearylene having from 13 to 16 carbon atoms.
 22. A processaccording to claim 21, wherein the starting material is a prepolymerwhereinR is lower alkylene having up to 6 carbon atoms, p is zero and R³is alkenyl having from 2 to 8 carbon atoms.
 23. A process according toclaim 21, wherein the starting material is a prepolymer whereinR islower alkylene having up to 6 carbon atoms, p is one, q is zero, R⁵ islower alkylene having from 2 to 6 carbon atoms and R³ is alkenyl havingfrom 2 to 8 carbon atoms.
 24. A process according to claim 21, whereinthe starting material is a prepolymer whereinR is lower alkylene havingup to 6 carbon atoms, p is one, q is one, R⁴ is lower alkylene havingfrom 2 to 6 carbon atoms, phenylene, unsubstituted or substituted bylower alkyl, cyclohexylene or cyclohexylene-lower alkylene,unsubstituted or substituted by lower alkyl, phenylene-lower alkylene,lower alkylene-phenylene or phenylene-lower alkylene-phenylene, R⁵ islower alkylene having from 2 to 6 carbon atoms and R³ is alkenyl havingfrom 2 to 8 carbon atoms.
 25. A process according to claim 17, whereinthe starting material is a derivative of a polyvinyl alcohol having amolecular weight of at least about 2000 that, based on the number ofhydroxy groups of the polyvinyl alcohol, comprises from approximately 1to approximately 15% of units of formula I.
 26. A device for themanufacture of mouldings havinga closable and openable mould, the mouldcomprising shape-forming surfaces that form a mould cavity when themould is closed, which mould is intended to receive a crosslinkablestarting material and is at least partially permeable to energy thatcauses the crosslinking of the starting material and is supplied fromthe outside; means for filling the mould cavity; an energy source; andmeans for the impingement of the energy upon the mould,wherein theshape-forming surfaces of the mould cavity are continuously immersed inthe starting material during the manufacture of the moulding.
 27. Adevice according to claim 26, which comprises a reservoir for supplyingthe starting material, which reservoir surrounds the mould cavity and iscapable of being connected to the mould cavity, and wherein duringfilling of the mould cavity the reservoir is connected to the mouldcavity and floods that cavity.
 28. A device according to claim 26, whichcomprises means closing the mould arranged in the starting material. 29.A device according to claim 26, wherein the mould comprises a containerand a mould member displaceable in that container, which mould membercan be moved away from and towards the container wall lying opposite itfor the purpose of opening and closing the mould, and wherein there isprovided in the container an inlet through which starting material flowsin between the container wall and the mould member as the mould isopened, and wherein there is provided in the container an outlet throughwhich starting material flows out again as the mould is closed.
 30. Adevice according to claim 29, wherein the mould comprises two mouldhalves, one mould half being provided on the container wall and theother on the displaceable mould member.
 31. A device according to claim30, wherein the mould comprises a male mould half and a female mouldhalf, and wherein the male mould half is provided on the container walland the female mould half is provided on the displaceable mould member.32. A device according to claim 29, wherein pumps are provided which, asthe mould is opened, feed in starting material through the inlet andbetween the container wall and the mould member and, as the mould isclosed, convey starting material away again through the outlet.
 33. Adevice according to claim 29, wherein means are provided for driving thedisplaceable mould member.
 34. A device according to claim 26, whereinmeans are provided for producing a flow that separates the moulding fromthe mould when the mould is opened and flushes the moulding out of themould when the mould is closed.
 35. A device according to claim 26,wherein a gripping device is provided which removes the crosslinkedmoulding from the mould.
 36. A device according to claim 29, wherein thecontainer comprises, on a container wall other than the shape-givingface, a hollow or recess that extends substantially in the direction ofmovement of the displaceable mould member, a gripping device beingarranged in that hollow or recess, and wherein the displaceable mouldmember comprises, on an outer wall that does not lie opposite theshape-giving container wall, an indentation in which the gripping devicedeposits the removed moulding.
 37. A device according to claim 36,wherein the displaceable mould member comprises a channel that leads tothe indentation and can be connected to a negative pressure or positivepressure source, which channel is connected to the negative pressuresource when the gripping device deposits the removed moulding in theindentation of the mould member and then is connected to the positivepressure source in order to release the lens.
 38. A device according toclaim 30, wherein the mould is provided with spacers that hold the twomould halves a small distance apart from one another when the mould isin the closed position, so that an annular gap is formed that surroundsthe mould cavity and is in communication with that cavity.
 39. A deviceaccording to claim 38, wherein the mould is provided with resilientmeans or displacement means that allow the two mould halves to movecloser together following crosslinking shrinkage.
 40. A processaccording to claim 8, wherein the moulding is separated from the mouldby the flow of starting material as the mould is opened and is flushedout of the mould by the flow of starting material as the mould isclosed.
 41. A process according to claim 11, wherein the mouldingremoved from the mould by the gripping device is deposited on thedisplaceable mould member outside the space between the displaceablemould member and the opposite-lying container wall.
 42. A deviceaccording to claim 35, wherein the container comprises, on a containerwall other than the shape-giving face, a hollow or recess that extendssubstantially in the direction of movement of the displaceable mouldmember, the gripping device being arranged in that hollow or recess, andwherein the displaceable mould member comprises, on an outer wall thatdoes not lie opposite the shape-giving container wall, an indentation inwhich the gripping device deposits the removed moulding.
 43. A processof claim 1, wherein the moulding is an optical lens.
 44. A process ofclaim 43, wherein the moulding is a contact lens.
 45. A process of claim18, wherein R³ is an olefinically unsaturated copolymerisable radicalhaving from 2 to 8 carbon atoms.
 46. A process of claim 45, wherein R³is an olefinically unsaturated copolymerisable radical having from 2 to4 carbon atoms.
 47. A process of claim 20, wherein R³ is an olefinicallyunsaturated copolymerisable radical having from 2 to 8 carbon atoms. 48.A process of claim 47, wherein R³ is an olefinically unsaturatedcopolymerisable radical having from 2 to 4 carbon atoms.
 49. A processfor the manufacture of a molding, comprising the steps of:(1) providinga male mold half having a first shape-forming surface and a female moldhalf having a second shape-forming surface, which shape-forming surfacesform a mold cavity when mated, wherein said mold is at least partiallypermeable to the crosslinking energy; (2) introducing a startingmaterial, which is crosslinkable by the impingement of suitable energy,into said mold cavity while said shape-forming surfaces of the moldhalves are continuously immersed in the starting material during theintroducing step, thereby inhibiting the formation of bubbles in saidmold cavity; (3) mating said male and female mold halves to form saidmold cavity; and (4) impinging crosslinking energy upon the startingmaterial in said mold cavity, thereby forming a molding.
 50. A processof claim 49, wherein said molding is an optical lens.
 51. A process ofclaim 50, wherein said molding is a contact lens.
 52. A process of claim49, wherein the entire face of the female mold half which includes theshape-forming surface of the female mold half and the entire face of themale mold half which includes the shape-forming surface of the male moldhalf are continuously immersed in said starting material during saidprocess, thereby eliminating inclusion of bubbles in the startingmaterial in the mold cavity which results from contact of ashape-forming surface with the surrounding atmosphere.
 53. A process ofclaim 49, wherein said female mold half is affixed to the bottom of acontainer holding said starting material, and said male mold half isaffixed to a means for displacing said male mold half relative to saidfemale mold half, wherein said mating step comprises displacing saidmale mold half towards said female mold half until a mating position isachieved.
 54. A process of claim 49, wherein said male mold half isaffixed to the bottom of a container holding said starting material, andsaid female mold half is affixed to a means for displacing said femalemold half relative to said male mold half, wherein said mating stepcomprises displacing said female mold half towards said male mold halfuntil a mating position is achieved.